Unconfined Compressive Strength Research Articles

Impact of long-term depletion on horizontal wellbore stability in tight reservoirs-including changes in petrophysical and geomechanical properties

The development of tight reservoirs using a horizontal well requires caution owing to the reservoir sensitivity to stress. Predicting the horizontal wellbore instability during reservoir depletion is critical for tight reservoirs. The present study investigated the wellbore failure criteria and stress orientation changes with reservoir depletion of a horizontal well in a tight reservoir, considering rock sensitivity to stress with pressure reduction. An integrated reservoir model coupled with geomechanics was used to predict pore pressure. A mechanical earth model (MEM) was constructed to examine the stability of horizontal wells. The unconfined compressive strength (UCS) was correlated with changes in porosity due to stress changes. The MEM shows that the failure criteria around the horizontal wellbore, including breakout, loss, and breakdown pressures, change considerably with reservoir depletion. A more significant response was observed in the stress-sensitive layer, which was characterised by a higher permeability. The safe mud weight window of the studied horizontal well narrowed significantly after production for five years, whereas the stability was completely absent after ten years. The deterioration of stability with depletion is governed mainly by permeability reduction, which may cause severe pressure reduction, whereas the stability improvement due to the increase in UCS caused by porosity reduction seems marginal. Relatively small changes in the direction of the stresses around the wellbore with depletion were observed, with the stress distribution concentrated in the predominant direction as the depletion continued. This study indicates that the sensitivity of petrophysical and geomechanical properties to stress amplifies the instability in tight reservoirs, particularly around wellbores.

Combined effect of fiber and degree of stabilization on the early age behavior of cement bound granular mixtures

Abstract An investigation has been undertaken to study the effect of fiber-reinforcement and different degrees of stabilization on the early age mechanical behavior of cement bound granular mixtures intended to be used as a base layer within pavement structure. Waste plastic fibers (WPF) recycled from soft drink bottles were used at 1% by the mass of aggregate to reinforce cemented mixtures. To stabilize different mixtures, cement content of 3%, 5%, and 7% by the mass of aggregate and by the weight of aggregate and fiber were used for conventional and fiber-reinforced cement bound granular mixture (CCBGM& FRCBGM), respectively. The examined properties include unconfined compressive strength (UCS), indirect tensile strength (ITS), bulk density, and ultrasonic pulse velocity (UPV). The results showed a significant improvement in UCS and ITS as the cement amount increased for both types of mixtures. Incorporating PET fibers at cement content of 5% and 7% resulted in a noticeable improvement of ITS compared to the conventional mixtures while a marginal enhancement in the UCS occurred due to fiber-reinforcement. Both bulk density and UPV were increased as cement content increased, while both were decreased due to the inclusion of waste plastic fibers (WPF). Hence, utilizing waste plastic fiber has a positive and promising effect on the pavement structure from sustainability, integrity, and economic points of view.

Analysis of strength characteristics and microstructure of alkali-activated slag cement fluidized solidified soil

In order to solve such as difficulties in backfilling narrow foundation trenches in engineering, it was proposed to use alkali-activated slag cement (AASC) instead of traditional Portland cement to solidify silt and form AASC fluidized solidified soil. The effect of the content of AASC and the curing period on fluidized solidified soil has been studied by unconfined compression strength test, SEM and EDS. Moreover, the root cause for the improvement of the strength by the microstructure was explored. The results showed that: The fluidity increased first and then decreased with the increase of the content of AASC; 40% was the optimal content; in the same curing period, the unconfined compression strength increased with the increase of the content; 40% was the optimal content; the soil with different contents could reach the most of the 28d strength on Day 7; AASC generated a lot of low-Ca/Si C-S-H gel that consolidated soil particles into a denser structure. These results provide a theoretical basis for the application of AASC in fluidized solidified soil engineering.

Experimental study on the performance of shield tunnel tail grout in ground

Shield tail grouting is an important measure to control tunnelling-induced ground deformation by injecting prepared grouting materials to fill the tail gap. The working performance of grout is usually invisible and hard to obtain in construction. This paper carries out an experimental study to investigate the tail grout behavior in ground. In the current research, a testing device is developed to explore the grout behavior in varying soils. The grout working performance is evaluated not only by the liquid grout properties such as fluidity, consistency, bleeding rate, stone rate and compressed deformation but also solid grout properties such as unconfined compressive strength and permeability. Three typical grouts are chosen and their behaviors in the various soils are observed. To take an insight on the behaviors, scanning electron microscopy and mercury intrusion porosimetry analysis are employed. The microstructure of solid grout is a sign of its working performance. The observation shows that the solid grout micro-structure is influenced by grout proportions, pressure, and ground permeabilities. The experimental results are applied in the case of Beijing Metro Line 12 for validation and as a result, the ground movement is inhibited due to high performance of tail grout.

Experimental study on the effects of composite reinforcement of ionic soil stabilizer and sand on bentonite

This paper utilizes both the ionic soil stabilizer (ISS) and sand to strengthen bentonite, as ISS effectively reduces its expansive properties and sand rapidly improves its strength to reduce cracks. Various experiments are conducted to analyze the changes in physical and mechanical properties of the bentonite strengthened by ISS-sand (ISB). The results show that not only do the sand particles enhance the strength of bentonite, but also the ISS significantly reduces its expansibility. Furthermore, the mass ratio of sand to bentonite has different effects on the unconfined compressive strength (UCS) and the freeze-tolerance of sand-reinforced bentonite (SB) and ISB. These findings suggest that a comprehensive consideration of the sand mixing rate is necessary when implementing ISS reinforcement on natural expansive soil.

Enhancing Soil Stability through Innovative Microbial-Induced Calcium Carbonate Techniques with Sustainable Ingredient

Expansive soil poses significant challenges for civil engineers, leading to structural damage, particularly in lightly loaded structures. This study employs an innovative and sustainable recipe to stabilize highly expansive soil using the Microbial-Induced Calcium Carbonate Precipitation (MICP) technique by substituting conventional ingredients with olive mill wastewater and hydrated lime. A series of laboratory tests were performed to evaluate the improvement in Atterberg's limits, Free Swell, Unconfined Compressive Strength (UCS), and pH, in addition to a series of qualitative measurements, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Optical Microscopic Images, and bacteria growth rate. Different mellowing periods and different cementation concentrations were used. The proposed recipe results showed a 50% reduction in the soil's free swell value. The UCS of the treated soil using the proposed recipe was eight times that of the untreated soil and twice that of the soil treated with the traditional recipe. The SEM images showed flocculation and aggregation in the soil particles, with the voids becoming smaller and filled with calcium carbonate (CaCO3). The XRD results showed the formation of new CaCO3particles. The optimized recipe demonstrated remarkable enhancement improvement and significant changes in soil physical properties and microstructure. Doi: 10.28991/CEJ-2024-010-08-08 Full Text: PDF

Effects of specimen size and loading rate on the mechanical property of Bentonil-WRK bentonite for engineered barrier system

This study aims to investigate the effects of specimen size and loading rate on the mechanical property of Bentonil-WRK bentonite buffer material for engineered barrier system. Highly instrumented unconfined compressive strength tests were performed on cylindrical specimens prepared using cold isostatic pressing (CIP) technique at varying testing conditions: (a) CIP pressures of 29.43 MPa, 39.24 MPa, and 58.86 MPa, (b) specimen sizes of 30 × 60mm, 40 × 80mm, and 50 × 100mm, and (c) loading rates of 0.5 %/min, 1.0 %/min, and 1.5 %/min. As CIP pressure increases, the unconfined compressive strength (qu), failure strain (εf), and elastic modulus (E) of Bentonil-WRK increase similar to Gyeongju compacted bentonite (KJ-II). Increase in diameter results in a decrease in qu and εf, and increase in E. Minimal effect of loading rate was observed on qu and εf. However, increasing loading rate tends to increase E. In addition, decrease in diameter increases the elastic threshold axial strain (εe,th). Increase in diameter and loading rate slightly increases Poisson's ratio. Prediction models are provided for assessing the effects of specimen diameter on qu and εf. Furthermore, correlation models of qu to ρd and E are proposed for Bentonil-WRK bentonite buffer material.

Exploring sustainable solutions for soil stabilization through explainable Gaussian process-assisted multi-objective optimization

The adoption of sustainable solutions in soil stabilization has piqued the interest of the scientific community due to the potential reduction in carbon footprint. In this regard, the research community has started looking for the alternate sustainable solutions to limit the quantity of conventionally used ecologically unfriendly soil stabilizers like lime and cement by utilizing the agricultural and industrial by-products. The production of conventional soil stabilizers (lime and cement) is extremely energy-intensive and contributes tons of greenhouse gases to the atmosphere. In general, evaluating suitability of these additives requires in-lab investigation of soil samples with varying additive concentrations and curing periods, making this approach both resource and time-intensive. Hence, this article proposes a computational framework for accelerated characterization of soil-stabilization by using the coupled experimental-Gaussian process (GP) based machine learning (ML) model. The dataset utilized for constructing the GP models consists of input features such as the stabilizer content (lime and rice husk ash (RHA)), coir fiber content, and curing period (measured in days). The target responses are the strength measures of the stabilized soil, such as unconfined compressive strength (UCS), split tensile strength (STS), and California bearing ratio (CBR). The proposed computational framework is deployed to perform multi-objective genetic algorithm (MOGA)-based optimization to achieve maximum engineering performance from stabilized soil. The presented study demonstrated that with the optimal dosage of rice husk ash (agricultural by-product), and cashew nut shell liquid (CNSL) treated coir fiber, the requirement for lime dosage may be significantly reduced while maintaining the engineering performance of the soil. The presented computational framework can be extended to any construction practices for ensuring the strategic selection of the control variables for optimizing the desired performance.

Influence of adding gypsum on the properties of lime-stabilized expansive soil

Abstract Expansive soils present major structural and geotechnical engineering problems. Expansive soil undergoes considerable changes in volume because of variations in water content. These variations in volume can occur as either swelling or shrinking and are commonly referred to as swell-shrink soils. Considering key aspects, such as the characteristics of the soil, is essential when dealing with swelling soils. There are expansive soils in both humid areas, where they pose problems with a high plasticity index, and in semi-arid or arid areas, where even moderately swelling soils can cause considerable damage. In order to solve problems related to expansive soil, it is important to stabilize it using various additives like gypsum, lime, and so on. The effects of adding three percentages of gypsum (2%, 4%, and 8%) to 6% lime-stabilized expansive soil to improve its engineering properties are investigated through several tests. The results of tests displayed that adding gypsum has improved properties of prepared soil with 6% lime. The optimum mixture for (gypsum-lime) that gets the highest improvement in soil properties is (6% lime + 4% gypsum). This mixture shows reducing in the free swell, swelling pressure, and plasticity index (from 8.51% to 2.81%, from 715.68 Kpa to 89.18 Kpa, from 33% to 29% respectively). Also, this mixture shows increasing in CBR (from 13.69% to 16.17%) and unconfined compressive strength (UCS) for the curing time of 0, 7, and 14 days (from 264.318 Kpa to 492.131 Kpa, from 380.584 Kpa to 736.318 Kpa, and from 480.192 Kpa to 828.590 Kpa respectively). The maximum dry density (MDD) and optimum moisture content (OMC) increase with increasing gypsum content, While the specific gravity decreases.

A Novel Multiple Linear Regression Approach for Predicting the Unconfined Compressive Strength of Soil

A Novel Multiple Linear Regression Approach for Predicting the Unconfined Compressive Strength of Soil

Bio-Electrokinetic Improvement of Deltaic Soil

In addressing problematic soils, geotechnical engineers employ two key strategies: compatibility and improvement. This study focuses on soft and CL deltaic sediments, and seeks to enhance cementation by investigating microbially-induced calcium carbonate precipitation (MICP). Sporosarcina pasteurii bacteria, together with a cementation solution (urea and calcium-containing salt), were electrokinetically injected into deltaic clay soil from the Telar River in Iran. The initial samples, with a dry unit weight (γd) of 12.75 kN/m³, underwent injections in two modes: simultaneous injection of the bacterial and cementation solutions and individual injection in a sequential order. Unconfined compression strength tests and laboratory vane shear tests were conducted to assess changes in soil strength parameters, while a consolidation test was performed to investigate alterations in soil settlement parameters. A comparative analysis with an electroosmosis control sample revealed a remarkable increase in compressive strength and undrained shear strength for MICP bio-electrokinetic improvement. Moreover, the consolidation test demonstrated that the compression index (Cc) and recompression index (Cr) exhibited a more pronounced decline in the simultaneous injection than individual injection. This highlights the dual impact of the bio-electrokinetic method, namely the enhancement of shear strength and the mitigation of settlement in deltaic clay soil. The calcium carbonate content was measured for the samples, and the results indicated a higher degree of participation for the samples subjected to simultaneous injection. Microstructure analyses were conducted on samples, and calcite and vaterite were observed in bio-cemented samples.

Exploring the Potential of Native Urease-Producing Bacteria of Hilly Terrain for Soil Strength Enhancement

Bio-cementation of weathered soils of hilly regions using native ureolytic bacteria is a practical approach to improve soil strength. This study aimed to isolate and characterize native urease-producing bacterial strains from different slope failure regions of Uttarakhand, India, through multi-step screening, and showcased their potential in soil improvement. A total of 80 bacterial strains were isolated from thirteen landslide-prone sites to screen for potent native urease-producing strains. Interestingly, nine native strains exhibited high calcium carbonate precipitation (158–187 mg/10 ml) and urease activity (657–3495 µM/mL) compared to Sporosarcina pasteurii (NCIM 2477), a potent bacterium commonly used for bio-cementation. These strains belonged to various genera, including Lysinibacillus sp., Sporosarcina sp., Pseudochrobactrum sp., and Cytobacillus sp. Cohesionless soil samples treated with the native strains exhibited high unconfined compressive strength values ranging from 0.1 MPa to 1 MPa, whereas those treated with S. pasteurii were 0.15 MPa. The urease-producing bacterial strains with CaCO3 precipitation activity influenced the soil strength and failure patterns. FESEM, XRD, and acid-washing tests revealed that native bacterial strains precipitated CaCO3 more than S. pasteurii strain. The study explores, for the first time, the potential of native ureolytic bacteria from different regions of Uttarakhand, India, for soil strength enhancement.

Investigation of the effect of relative humidity on micro lime consolidation of degraded earthen structures

Micro lime, hydrated lime (Ca (OH)2) with particle sizes of 1-3μ dispersed in isopropanol, can be used to reinforce deteriorated earthen structures. The consolidation effect depends on the amount of moisture present in the structure or in the ambient air. This study investigates the influence of different levels of relative humidity (RH) on the consolidation effect of micro lime on earthen structures, the chemical processes responsible for the consolidation and the physical changes to the structure. The aim is to gain a deeper understanding of the underlying chemical reactions and to identify a potential limit to the applicability of this consolidation method in low RH environments. The fact that many of these sites are located in arid climates greatly influences the practical application of micro lime in the conservation of historical earthen structures. To characterize the consolidation effect of micro lime, unconfined compressive strength and exposure to wet and dry cycles were used. The properties of the reaction products and the bonding between soil particles and micro lime were investigated using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). At RH levels of 25%, 45%, 65% and 90%, the unconfined compressive strength (UCS) and the modulus of deformation at 50% strength (E50) of the micro lime-reinforced specimens demonstrated an increase with humidity. This led to a significant improvement in their ability to resist the effects of dry–wet cycles. Results from thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) indicate that micro lime interacts with the soil matrix via carbonation, with the reaction rate increasing with humidity. At 25% RH, vaterite was produced and residual free lime was observed, whereas at humidity levels of 45% and above, the reaction yielded vaterite and aragonite. The lime treatment did not significantly alter the pore structure of the soil specimens. The total porosity of the specimens was only slightly reduced, with the main effect of the lime treatment being a reduction in the number of large pores.

Strength Evaluation of Clayey Sand Admixed with Wollostonite with A Special Reference To Construction of Geotextile Reinforced Subgrade

Objectives: To enhance the performance of subgrade constructed using Clayey sand. Clayey sand is a commonly found inferior soil and it is made to be suitable for flexible pavement construction. This study is intended to make Clayey sand suitable by admixing with Wollastonite and embedding with geotextile reinforcement. Methods: The study involved laboratory tests to determine the optimal dosage of Wollastonite to stabilize clayey sand. Tests included Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) evaluations. Subsequently, geotextile reinforcement was incorporated with the Wollastonite-stabilized soil to further enhance its strength characteristics. Findings: The research revealed that Clayey sand, in its original form, is unsuitable for subgrade construction due to its poor strength properties. Admixing with Wollastonite significantly improved its strength and expected performance was observed at a specific dosage. Further enhancement was achieved by embedding geotextile reinforcement, which increased both UCS and CBR values. The combination of Wollastonite stabilization and geotextile reinforcement yielded requisite strength for Clayey Sand with respect to strength and stability thus making it suitable for subgrade construction of the flexible pavement. These findings are consistent with existing literature on soil stabilization techniques, but the usage of Wollastonite and geotextile in this context presents a novel approach. The results highlight the potential of this method to address the scarcity of suitable subgrade soils, offering a viable solution for pavement construction projects with inferior soils. Novelty: The study introduces Wollastonite and geotextile reinforcement as effective methods to stabilize and enhance the strength of Clayey sand for subgrade construction in flexible pavements. Keywords: Soil Stabilization, Clayey Sand, Subgrade, Wollostonite, Geotextile, Unconfined Compressive Strength, California Bearing Ratio

Accelerated carbonation of non-plastic soils mixed with hydrated lime: index properties influencing binder formation rate and mechanical improvement

Chemical stabilization—the mixing of additives like cement, lime, or fly-ash with soil to improve its mechanical properties—conventionally relies on hydration reactions to generate a binder. Accelerated soil carbonation is a nascent alternative method, whereby carbon dioxide is intentionally introduced in soil mixed with alkali additives to generate a carbonate binder and sequester carbon dioxide. Non-plastic sand and silt specimens mixed with hydrated lime were carbonated for varying amounts of time at different water contents and densities to evaluate the index properties influencing the rate of carbonation and degree of mechanical improvement. It was demonstrated that volumetric air and water contents primarily govern the rate of binder formation and that mechanical properties are influenced by the carbonate binder content and density. Under optimum conditions, soil specimens could be fully carbonated within 3 to 24 hours and unconfined compressive strengths as great as 3 to 4 MPa were achieved. The degree of strength improvement is comparable to cement-stabilized materials with similar dependence on soil type, density, and binder content. If techniques are developed that enable carbonation at scale, the sequestration of carbon dioxide would offset emissions associated with production of chemical additives used for chemical stabilization.

Low-carbon metakaolin precursor for one-part and two-part geopolymer activation of demolition wastes

A critical part of civil engineering infrastructure works is to develop innovative construction materials for a low-carbon future development. This study delved into the feasibility of using metakaolin (MK) as a low-carbon precursor for one-part and two-part geopolymer stabilization of recycled demolition wastes. In this research, the effects of MK precursor were evaluated in combination with construction and demolition (C&D) waste aggregates such as crushed brick (CB), reclaimed asphalt (RAP) and recycled concrete (RCA) using one-part and two-part geopolymer activation. Various geotechnical tests were performed including compaction tests, repeated triaxial loading tests (RLT), unconfined compressive strength tests (UCS) and microstructural analysis. Results from this study indicated significant strength development of MK mixtures for both one-part and two-part geopolymer options. Furthermore, one-part geopolymer also showed better activation than two-part geopolymer under 7 days and 20℃ curing condition. Additionally, 30 % MK mixtures were optimal for road construction applications based on the obtained results. At 28 days or 40 ℃, MK mixtures performed best with RCA and CB as main aggregates, showing strength improvement of up to 250 % compared to 7 days and 20 ℃ curing condition. Resilient modulus (Mr) results indicated that the optimal mixtures experienced good resilient behavior with average Mr values ranging from 150 MPa to 200 MPa. Overall, MK precursor was found to be a suitable material for stabilizing demolition aggregates using geopolymer under various curing conditions.

An approach for strength development assessment of cement-stabilized soils with various sand and fine contents

Cement stabilization is a well-established ground improvement technique. However, there have been limited investigations aimed at the effect of heterogeneous soil types with varying amounts of coarse-grained (sand) and fine-grained (silt and clay) substances, on the strength enhancement of cement-stabilized soils. In this cement stabilization research study, sand (S) and clayey silt (F) were mixed together to have a variety between coarse- and fine-grained fractions at 100, 75, 50, 25, and 0 % by dry weight, designated as the ratio of S:F=100:0, 75:25, 50:50, 25:75, and 0:100, respectively. The water content was prepared at the range of 1.25–2.50 optimal water content to simulate field applications. The strength enhancement of cement-stabilized soils was influenced by the fine content, water content, and cement content. The soil–water to cement ratio (s-w/c) was effectively incorporate the impact of both water and cement contents on the strength enhancement, for a given a specific fine content. The generalized correlation between unconfined compressive strength, qu and s-w/c could be represented as a power function: qu = M/(s-w/c)N. In this equation, M and N are constants that are primarily influenced by the fine content. The shear strength ratio versus fine content chart was proposed as a means to assess the effect of fine content on the strength of cement-stabilized soil with varying s-w/c. A stepwise approach for assessing the strength enhancement of cement stabilization in soil based on physical characteristics (i.e., plasticity index and fine content) was proposed and validated. The robustness of the proposed approach was realized by the low mean absolute percent error, (MAPE<7.0 %) and high coefficient of determination (R2 > 0.95) for measured and predicted strengths comparison. This technique serves as a valuable tool for mix design, specifically in relation to clay mineral and fine content. It supports in making engineering decision regarding the appropriate amount of water and cement needed to achieve strength requirements throughout the requisite curing period, while minimizing the number of repetitions needed.

Effects of Palm Kernel Shells (PKS) on Mechanical and Physical Properties of Fine Lateritic Soils Developed on Basalt in Bangangté (West Cameroon): Significance for Pavement Application

The utilization of an agricultural waste product known as palm kernel shells (PKS) combined with fine laterites (from basalt in Bangangté, West Cameroon) to produce low-cost and innovative materials with good bearing capacities for road pavement was investigated. Fine laterites from two soil profiles (BL31 and BL32) and made up of kaolinite, hematite, goethite, gibbsite, anatase, ilmenite and magnetite minerals were partially replaced with PKS at 15%, 25%, 35%, and 45% by weight. Physical and mechanical tests, including particle size distribution, Atterberg limits, unsoaked and soaked California Bearing Ratio (UCBR and SCBR), unconfined compressive strength (UCS), and tensile strength (Rt), were performed on the different mixtures. After the addition of PKS, a decrease in fine particle content (77 to 38%), liquidity limit (LL: 72 to 61%), plasticity index (PI: 30 to 19%), maximum dry density (MDD: 1.685 to 1.29 t/m3), and optimum moisture content (OMC: 27.5 to 24.0%) was noticed. Additionally, there was an increase in UCBR (16–72%), SCBR (14–66%), UCS (1.07–7.67 MPa), and Rt (2.24–9.71 MPa). This allows new materials suitable for the construction of base layers for low trafficked roads (T1–T2), as well as sub-base and base layers for high trafficked roads (T3), to be obtained. This newly formed material can be recommended locally for road construction works, though more in-depth studies are required.

Effects of different Mg/Ca molar ratio on the formation of carbonate minerals in microbially induced carbonate precipitation (MICP) process

Traditional MICP technology has been extensively applied to improve soil properties and solidify heavy metal contaminated soil. However, the traditional product performance of calcite is far less than that of huntite, dolomite, and other carbonate minerals. Therefore, the soil strength and environmental safety after curing cannot reach the safety index. This study has examined the distribution of carbonate minerals induced by microorganisms under different Mg/Ca ratio. Compared with the sample with 0 Mg/Ca content, the unconfined compressive strength (UCS) can be increased by 1–5 times by increasing the content. By X-ray diffraction (XRD) and thermogravimetric analysis (TGA), the contents of different carbonate minerals under different Mg/Ca content were determined semi-quantitatively. The microscopic results have also shown that the introduction of microorganisms can provide nucleation sites for the synthesis of dolomite and huntite. MICP experiment coupled with Quantum ESPRESSO calculations revealed the mechanism of microbial influence on the formation of carbonate minerals under different Mg/Ca conditions through first principles calculations and nucleation kinetics. These findings advance our understanding of the reaction mechanisms and pathways of biogenic precipitation of carbonate minerals, and provide insights into the artificial quantitative synthesis of dolomite.

Rebuilding with sand roses: Cold sintering of sand-gypsum mixture for sustainable brick production

In the arid climate of the Sahara Desert, several historical cities dating back to the 16th century were constructed using bricks made from sand roses, a rosette-like rock composed of sand and gypsum. This study proposes the cold sintering of sand – dihydrate gypsum (uncalcined) mixtures as a sustainable approach to develop geomimetic sand roses with satisfactory mechanical performance. The results showed that crucial factors for enhancing the unconfined compressive strength (UCS) of the cold-sintered sand-gypsum mixtures are reducing gypsum size, utilizing cyclic loading, and applying higher pressures. Reducing sand size or introducing lubricant has minimal or negative effects. Cold-sintered sand-gypsum mixtures containing over 30 % micron-sized gypsum, subjected to cyclic pressures of 100 MPa for 15 minutes, can achieve superior UCS values compared to equidimensional concrete bricks. In addition, coating the mixture with calcium carbonate can be a viable approach for protecting against weathering agents. Coating and recycling the sand-gypsum mixture do not compromise the mechanical performance of the bricks. The proposed integration of sustainable materials and manufacturing practices has the potential to reduce costs, energy consumption, and industrial emissions, while promoting a circular economy and resource preservation. The proposed brick is referred to as “sand rose brick.”